The amount of time infant rats 3-13 days old spent emitting ultrasounds was greater when pups were placed in an empty dish than when placed in a dish containing clean bedding or soiled bedding from the nest. Pups from 5-13 days of age vocalized more when on the clean bedding than when on the soiled bedding. When placed on cloth covered dishes, pups vocalized most to the empty dish and least to the dish containing soiled bedding. The odor of clean bedding elicited less ultrasonic vocalization than the odor of the empty dish only when less than 7 days old. Pups vocalized more to room temperature than to heated conditions. The results indicate that olfactory, tactual, and thermal nest cues influence infantile ultrasonic vocalization in the rat.

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MEIER, GILBERT W., and SCHUTZMAN, LLOYD H. (1968). Mother-infant Interactions ond Experimental MonipulationrConfounding or Misidentification? DEVELOPMENTAL PSYCHOBIOLOGY, l(2): 141-145. T h e role of material responsiveness to offspring behaviors in the research on early experience and behavioral development is discussed. T h e proposition is offered that the behavioral changes following experimenter nianipulation of the offspring during the preweaning period, as by handling. isolation, shock stimulation, or cold stress, are attributable to the altered interaction between mother and infant, such that the mother responds diffcrentiallv to certain behaviors of her ofspring or predominantly to those offspring showing such behaviors. In support of this proposition, data are cited on preferential maternal responsiveness to infants by sex and the frequency is cnuincrated of significant Sex X Treatment interactions in thc early expcriencc studies.earl! experience maternal behavior sex differences N THE iNTERPRETATIoN of behavioral development

Four groups, two comprising three neonatal rhesus monkeys and two comprising two juvenile rhesus monkeys, were selectively deprived of either low‐voltage, fast‐wave sleep (LVF) or of high‐voltage, slow‐wave sleep (HVS), respectively. Both infant and juvenile Ss displayed an over‐all increase in threshold to the tone‐shock combination during the deprivation of either phase of sleep. However, the thresholds of the infant Ss were greater, throughout deprivation, than the thresholds of the juvenile Ss. The juvenile Ss exposed to LVF deprivation were unique in exhibiting a sharp increase in frequency of forced awakenings from LVF, to values significantly greater than for the other groups, and in displaying compensatory recovery effects, manifested by increases in proportion of total sleep time spent in LVF, following termination of deprivation. Behavioral disturbances accompanying deprivation were not evident in any of the experimental groups. The study revealed a number of methodological problems related to the definition and to the selective deprivation of a particular state of sleep.

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